After 1 ride at a track on new bike

Corrosion?? When was it manufactured?

What make and model is that thing?

Its dirt soaked into the castings. You can try mag wheel cleaner but the best way to get that off is vapor blasting. Scotch brite would have been my first choice but you tried it already.

Make a habit (next time) of washing your bike the same day as you get home. Some dirt is very corrosive and when it sits a day, or 3-4, it will do that.

Napa Alumibrite on a toothbrush very carefully will remove it. Rinse well. Might try soda blasting first though less aggressive..

Red scotch brite and bar keeps friend with water. Just need some elbow grease to get in there.

This happened to me on my 2009 KX450. I had the bike for about a month and was riding a track in the rain and tore a ligament in my ankle. I put my bike away without washing it and when I finally could wash it, the bike looked like this. I thought the bike was just stained from the dirt, but it actually oxidized the aluminum. Unfortunately I never found a way to get the bike looking new again...

I've had good luck with steel wool saturated with WD40 + elbow grease.

You could also likely use CLR, too, but I have no experience with this.

Its funny I had a 2010 Honda that never did this no matter how long between washes however I switched to Kawasaki from 2013-16 and every kawi did this really badly. All my newer Honda’s from 2017 up have been staining like your new one so I suspect Honda has lowered their quality of materials over the years. I use the soap pad steel wools although it doesn’t make it look new again.